WASHINGTON
— While in Pakistan to help break ground for a nuclear reactor, China's premier talks about enhancing bilateral nuclear cooperation by selling the country two more nuclear power plants.

The United States, as part of a stepped-up energy dialogue with India, suggests it could eventually sell India nuclear reactors - in part to keep it from going into the natural gas pipeline business with Iran.

And North Korea shuts down its nuclear reactor, which could mean it is planning to ramp up nuclear arms production - or just using routine maintenance to scare others about its nuclear ambitions.

All these events, spread over the past month, occur in a global context of "erosion of the nonproliferation regime [that] could become irreversible," a high-level United Nations panel recently concluded.

With the world community set to take up a five-year review of the Non-Proliferation Treaty (NPT) next week, experts point both to advances and to worrying signs to bolster a preponderant view that more must be done if a dangerous wave of proliferation is to be stopped.

He puts North Korea, which last year withdrew from the treaty and boasted of nuclear weapons, and Iran, an NPT signatory suspected of pursuing weapons development, as two black marks on the nonproliferation ledger. But he counts Libya's renunciation of its nuclear program, a recent UN resolution binding members to strict laws on nuclear-materials exports, and other added international safeguards as positive signs.

"Fundamentally the international community is rallying to the cause," Mr. Spector says, "so I'd imagine that if anything, [the treaty, after the May review] will be a little stronger."

Yet for others, the picture is darker - for reasons stretching beyond North Korea and Iran and ranging from developing countries' drive for cheaper, abundant, and nonpetroleum energy sources, to US moves to build replacement nuclear weapons.

"There's a lot of bad news," says Daryl Kimball, executive director of the Arms Control Association in Washington. His organization and the Carnegie Endowment for International Peace earlier this month issued a statement, signed by prominent former officials and nuclear-weapons experts, warning that the world is on the "threshold" of a new round of proliferation that next month's NPT review must address.

The review will be buffeted by events in Iran and North Korea.

Iran is expressing growing impatience in its talks with three European countries over its uranium-enrichment program. And by the time the review begins May 2, North Korea's intentions may be clearer. North Korean officials have said their intent is to obtain plutonium to fuel nuclear bombs, but whether that is mere rhetoric to focus world attention is unclear.

Existing global stockpiles of highly enriched uranium and plutonium - the fissile materials that fuel nuclear bombs - probably constitute the biggest threat to nonproliferation, experts say. And that is one reason the developing world's heightened interest in nuclear power is so worrisome, they add: In a decade or so, more reactors could result in a larger - and potentially less controllable - stockpile of raw materials.

That is why some find China's talk of supplying Pakistan with more nuclear reactors so alarming - especially given Pakistan's history as a supplier of the world's clandestine nuclear bazaar.

In recent Senate testimony, Robert Joseph, the administration's nominee for undersecretary of state for arms control and international security, said that the China-Pakistan nuclear cooperation under way is under international safeguards. He downplayed the likelihood of China pursuing additional projects with Pakistan.

But at the same time, another State Department official acknowledges that discussions between the two countries about additional nuclear reactors are "worrisome."

Others are still more categoric.

"This is a big concern," says Henry Sokolski, executive director of the Nonproliferation Policy Education Center. He points to Pakistan's refusal to sign on to an additional protocol to the NPT that calls for countries receiving new facilities to accept international safeguards, and cites Pakistan's history in supplying parts to international nuclear markets.

But the US has weakened its ability to object because of its own participation in the nuclear reactor marketplace, he says.

Pointing to a $5 billion deal for the Westinghouse Electric Co. to supply China with nuclear power plants, and to recent discussion by US officials of selling reactors to India, Mr. Sokolski says, "Either President Bush wasn't serious when he said [in 2004] that the additional protocol should be the condition for these sales, or we need to rethink what we are proposing to sell to China and to India."

Developing nations' insistence that they have a right to obtain nuclear technology as a source of energy is one issue the NPT review must confront. But some say that just as contentious is the US drive to build a new arsenal of replacement nuclear warheads.

"One of the key issues of the conference will be how the nuclear states are doing at fulfilling their own nuclear disarmament commitments," says the Arms Control Association's Mr. Kimball.

The administration wants to go ahead with feasibility studies that could result in a new generation of replacement warheads within a decade. But that runs contrary to disarmament commitments the US made at NPT reviews in 1995 and 2000, Kimball says. "For the US to ask others to take on additional commitments while disregarding its own commitments to the NPT is a recipe for division," he says. "You're basically assuring a lack of progress towards the very goals the US says it supports."